This proposal is for the design, construction and evaluation of an atmospheric ion focusing device for ultra-trace constituent mass detection of analytes eluting from a liquid chromatograph. The design is based on a novel focussing device whereby a highly dispersed plasma of gas-phase ions at atmospheric pressure are collected, enriched and transported to a sampling aperture. Unlike conventional atmospheric pressure ionization sources, such electrospray, atmospheric pressure ionization, inductively coupled plasma sources, where a highly charged dispersed aerosol is sampled through small aperture of capillary, this design first entrains and then enriches this highly dispersed aerosol by means of an electrical potential and a flowing gas stream before its is sampled. The applicants envisage the sensitivity of this high pressure focusing device will be superior to the present means of sampling ions generated at atmospheric pressure and introducing them into lower pressure regions of mass analyzers. This device as either and add-on to existing systems or incorporated into the designs of future systems will enhance the analysis of diagnostics measurements, toxicity studies and other laboratory and clinical applications currently not possible. PROPOSED COMMERCIAL APPLICATION: Atmospheric pressure ionization is one of the primary techniques for quantification and identification of biological and pharmaceutical applications. This atmospheric focusing device will make possible higher performance atmospheric pressure sources. The attributes of this focusing device are applicable to both high and low liquid flow atmospheric ionization systems as an add-on for existing systems, and as an integral part of the design of future atmospheric pressure ionization systems.